Viper User
Manual (001-5008-000 Rev6)
Page
59
The RTS threshold parameter specifies how large a packet must be before the unit will use
RTS/CTS handshaking in the over-the-air protocol. A value of 0 means the Viper will always
use over-the-air RTS/CTS handshaking. A value equal to the RF_MTU (OTA maximum
transmit unit) means the Viper will never use RTS/CTS handshaking. A value of 128 means
the Viper will use RTS/CTS for packets larger than 128 bytes.
Note: This should not be confused with RTS/CTS for RS232 Serial ports.
1.1.38
Carrier Sense Level Threshold
Default = -110 dBm. This is the threshold the Viper uses to determine whether a received
RF signal is a valid message or unwanted noise. If an RF level higher than the Carrier
Sense Level Threshold is detected, the Viper will attempt to decode the signal and will not
transmit until the RF level drops. Outgoing data will be buffered until the channel is
available. The carrier sense may be raised to prevent false carrier sense detection if the
network is installed in a noisy environment. In certain situations where the ambient RF
noise level is very low, the carrier sense level threshold can be lowered to gain extra receive
sensitivity. (The Viper's specified receive sensitivity depends upon the channel
bandwidth/speed being used. Refer to the product specification in Appendix A for details.)
1.1.39
Listen Before Transmit
Default = Enabled (listen to noise and data). The Viper radio has the ability to receive on
the Rx frequency to determine if the RF channel is busy. When the RF channel is busy the
Viper can buffer any data that needs to be sent over the air and will transmit when the RF
channel is free. There are three modes available in the Viper for the Listen Before Transmit
feature. They are described in the following paragraphs.
Enabled (listen to noise and data):
This is the default mode for the Viper. The Viper will
monitor the RF level on the receive channel. When the received level is above the carrier
sense threshold the Viper will try to receive and decode any and all messages from remote
Vipers. In this mode, the Viper will wait to transmit any data until the received level falls
below the carrier sense threshold. The received level will rise above the carrier sense
threshold due to several scenarios:
1) The Viper is receiving valid data
2) The Viper is not receiving data because two or more Vipers are transmitting at the
same time causing a collision
3) The Viper is not receiving data because the RF level is right at or below data
sensitivity or
4) There is interference from another RF system or electrical devices on the
frequency that the Viper is operating on.
In any of these scenarios, the Viper waits to transmit any data until the RF level falls below
the carrier sense threshold. This ensures that the data will have the best chance of
reaching its destination.
Enabled (listen to data only):
In this mode, the Viper will monitor the RF level on the
receive channel. When the received level is above the carrier sense threshold the Viper will
try to receive and decode any and all messages from remote Vipers.
When data is ready to transmit, the Viper will first check the receive level. If the receive
level is below the carrier sense threshold, the Viper will immediately transmit data. If the
